When hunter-gatherers in the Middle East began to settle down and cultivate crops about 10,500 years ago, they became the world’s first farmers. But two new papers suggest that they were at home on both the land and the sea: Studies of ancient and modern human DNA, including the first reported ancient DNA from early Middle Eastern farmers, indicate that agriculture spread to Europe via a coastal route, probably by farmers using boats to island hop across the Aegean and Mediterranean seas.
Archaeologists have long known that farming arose in the Middle East and then spread to Europe, because radiocarbon dating of hundreds of early sites shows a clear time gradient from east to west. But that is only a rough guide, and in recent years geneticists have been filling in the details of that picture by sequencing the DNA of both modern and ancient populations. While the relatively cool conditions at many European sites have helped preserve the DNA of ancient skeletons, researchers had not succeeded in sequencing DNA from the many skeletons found at very early Middle Eastern sites, due to their very hot and dry environments. That has left a big gap in their understanding of the very earliest steps in the spread of farming from the Middle East to Europe, which began at least 8000 years ago.
Since the early 1990s, a Spanish team has been excavating at three ancient farming sites in Syria, whose earliest dates range from 10,500 to 10,000 years ago—the very beginning of the agricultural revolution. Last week, in PLOS Genetics, the team reported having partially sequenced DNA from the mitochondria (the energy units of the living cell) of 15 skeletons from two of the sites, Tell Ramad and Tell Halula (see photo above). This is the first report of ancient DNA from early Middle Eastern farmers.
“It is clearly great that [genetic] data has become available” from these ancient groups, says Marie-France Deguilloux, a paleogeneticist from the University of Bordeaux in France, who adds that having such DNA sequences is “crucial” to tracing the spread of farming to Europe.
The paper’s lead author, anthropologist Eva Fernández of Liverpool John Moores University in the United Kingdom, attributes the team’s success to two main factors: First, the bodies at the Syrian farming villages were buried in pits under the floors of the houses and then sealed with thick mud, which probably protected the skeletons from the temperature extremes of Syrian summers; and second, the skeletons were put in cold storage immediately after being removed from the pits, which also preserved DNA from further degradation.
The mitochondrial DNA sequences from the Syrian skeletons showed what the team calls “strong affinities” with ancient DNA recently recovered from roughly 7000-year-old farming villages in both Germany and Spain, confirming that populations in the Middle East were indeed the source of later farming populations in Europe. Even more important, Fernández and her colleagues say, is what the team found when it compared the Middle Eastern DNA with a database of 60 modern populations in the Middle East and Europe. That analysis revealed very close genetic affinities with people living today in Cyprus and Crete, suggesting that farmers had first migrated from the Middle East to Greece and its islands by boat, before moving on to the mainland. The alternative, more northern route, overland to Europe via modern-day Turkey, was not supported by the data, because modern populations in Turkey did not show close genetic relationships to the Syrian skeletons.
Fernández says that this scenario is also bolstered by archaeological findings of the past couple of decades. Very early farming sites have been excavated on Cyprus, but researchers were not sure whether they represented a small population pushed off the mainland—perhaps by population pressure or competition with other farmers—or the beginnings of a major migration across the sea to Europe. “This implies that the first farmers were undoubtedly in possession of advanced enough navigation capabilities,” as well as adequate boats, to make the 60 kilometers sea voyage from the mainland, Fernández says.
More evidence that Middle Eastern farmers were also sailors comes from a paper published online today in the Proceedings of the National Academy of Sciences. A team led by George Stamatoyannopoulos, a geneticist at the University of Washington, Seattle, looked at 75,000 genetic markers across the genomes of 964 people from 32 different modern populations, including Greece and the Greek islands, Turkey, Europe, the Middle East, and North Africa. Using statistical techniques that allow researchers to trace the origins of populations based on the differences between them today, these researchers also found that farming had spread to Europe by a sea route, via Crete, the Greek islands, and the northern Mediterranean coast.
The two teams did differ on one question, however: whether Middle Eastern farmers first spread from the Levantine coast (modern day Israel, Lebanon, and Syria), the conclusion of the Fernández group; or from the southern coast of modern-day Turkey, as found by the Proceedings authors. Fernández says that while “both studies support each other” in pointing to a sea route, the differences between them could be due to the genetic profiles of Middle Easterners having changed since ancient times. In her view, the ancient DNA results from Syria would be a more reliable indicator of the genetics of early farmers.
However, outside researchers raise caution flags about the new ancient DNA findings. The sample of 15 skeletons from Syria is too small to represent all of the early Middle Eastern farming populations, says Guido Brandt, a paleogeneticist at the Johannes Gutenberg University Mainz in Germany. “It is questionable whether the genetic diversity of a melting pot like the [Middle] East can be sufficiently explored” by such a small number of partial mitochondrial DNA sequences, he contends.
Deguilloux agrees. Despite the strong evidence for a maritime spread of farming, she says, the current data cannot rule out the possibility that the spread of agriculture to Europe had “multiple origins,” including overland routes.